1. Field of the Invention
The present invention relates to an apparatus and method for controlling refrigerator defrosting.
2. Description of the Related Art
A conventional refrigerator has a closed refrigeration circuit including a cooling coil to cool compartments in the refrigerator, an expansion device, a radiation coil and a compressor. Refrigerant in the closed circuit is compressed by the compressor, then flows to the radiation coil. The compressed gaseous refrigerant, having a high temperature, is cooled in the radiation coil, and becomes liquid. The liquid refrigerant passes through the expansion valve, reducing its pressure and temperature. The cold liquid refrigerant flows into the cooling coil. Air passing through the compartments blows on the cooling coil and circulates in the compartments as a result of a circulation fan mounted in an air circulation path in the refrigerator. Therefore, the compartments are cooled. At the same time, liquid refrigerant in the cooling coil is heated by the air and evaporates. Energization of the circulation fan and compressor are controlled in accordance with the temperature in the compartments.
In the compartments, water included in the air as vapor is condensed on the cooling coil surface. The condensed water on the cooling coil surface becomes ice. The thermal conductivity of the cooling coil is decreased as a result of the ice. Further, the accumulation of ice reduces the amount of air passing by the coil. Consequently, the cooling capacity of the refrigerator is decreased and it is difficult to cool compartments. Therefore, the conventional refrigerator has a defrost operation to defrost the ice on the cooling coil.
In the defrost operation, the cooling coil is heated by an electrical defrost heater located near the cooling coil. The timing of the defrost operation is controlled by a defrost start timer. Two kinds of defrost timers are popularly used in conventional refrigerators. A first defrost timer measures time after a previous defrost operation is finished and outputs a defrost start signal when the time counted reaches a first predetermined time. A second defrost start timer measures the time that the compressor is energized and outputs the defrost start signal when that time reaches a second predetermined time.
Both of these defrost timers are reset when the defrost operation is finished. Accordingly, the defrost operation is carried out at intervals determined by the first or second defrost timer. The first and second predetermined times are constant values, and are determined for heavy load conditions when much vapor is included in the air. Thus, in the conventional refrigerator, the predetermined times between defrosts are set shorter than what is needed in normal or light conditions. Consequently, in normal or light conditions, where little or normal vapor is included in the air, defrost operations are started before they are necessary. As the frequency of defrost operations is increased, the energy consumption is increased, because the defrost heater is energized at every defrost operation. During the defrost operation, the temperature in the compartments of the refrigerator increases. As a result, food in the compartments can become spoiled.